The inventive subject matter relates to circuit breaker systems and methods and, more particularly, to shunt trip apparatus and methods.
Electric power switches, such as circuit breakers, transfer switches, disconnects and the like, may employ an electrically-activated shunt trip actuators that may be used to trip the operating mechanism of the switch. For example, circuit breakers may have shunt trip actuators that may be driven by control signals generated by external devices, such as fire alarm systems. The shunt trip actuator enables the fire alarm system to trip the circuit breaker to prevent damage and/or alleviate unsafe conditions. The breaker often can be manually reset after tripping.
Shunt trip actuators typically are implemented as flux transfer devices. Such devices use a spring to bias a plunger that engages the operating mechanism of the switch. A permanent magnet is used to counteract the spring force to maintain the plunger in an un-actuated position. A coil is configured to counteract the flux of the permanent magnet such that, when a current is passed through the coil, the permanent magnet field is interrupted, allowing the spring to force the plunger to the actuated position and open the breaker. Shunt trip actuator units typically impose requirements on the signals used to control them, i.e., the control signals have certain voltage and/or current requirements.